1. Field
Example embodiments generally relate to mechanical connections and methods. Example embodiments also relate to nuclear power plants and to mechanical connections and methods for repairing piping within reactor pressure vessels of the nuclear power plants.
2. Description of Related Art
Nuclear power plants may include filtered venting system to mitigate off-site release of radioactivity during a severe nuclear accident (e.g., partial or complete meltdown of reactor core, breach of reactor vessel by molten core debris) or any other time venting from the containment needs to be filtered (e.g., prolonged station blackout (“SBO”), loss of active containment heat removal capability, beyond-design-basis events). Such venting or depressurizations of the containment, whether from a wetwell or a drywell, may release radioactive materials in gaseous, liquid, and/or solid (e.g., particulate) form.
As would be understood by a person having ordinary skill in the art (“PHOSITA”), in the event of a severe nuclear accident, fission products may be released into the containment of the nuclear power plant. Of significant concern to the public are fission products of an aerosol nature, should such fission products escape the containment (according to the State-of-the-Art Report on Nuclear Aerosols dated Dec. 17, 2009, most radioactive material that may escape from a nuclear power plant during a severe nuclear accident will do so in the form of aerosols). Such fission products may include, for example, noble gases (e.g., krypton, xenon), halogens (e.g., bromine, iodine), alkali metals (e.g., cesium, potassium, rubidium), tellurium group (e.g., antimony, selenium, tellurium), barium, strontium, noble metals (e.g., cobalt, palladium, molybdenum, rhodium, ruthenium, technetium), cerium group (e.g., cerium, neptunium, plutonium), and lanthanides (e.g., americium, curium, europium, lanthanum, neodymium, nobelium, praseodymium, promethium, samarium, yttrium, zirconium).
Partially as a result of the Mar. 11, 2011, disaster at the Fukushima Dai-ichi Nuclear Power Plant site, the Nuclear Regulatory Commission (“NRC”) prescribed reliable hardened containment venting systems (“HCVS”) for many nuclear power plants (see NRC's “Order to Modify Licenses With Regard to Reliable Hardened Containment Vents, EA-12-050” dated Mar. 12, 2012). Such HCVSs may be required to include engineered filters (see NRC's “Order Modifying Licenses With Regard to Reliable Hardened Containment Vents Capable of Operation Under Seer Accident Conditions, EA-13-109” dated Jun. 6, 2013).
FIG. 1 is a block diagram of a related art system 100 for radioactive material capture.
As shown in FIG. 1, flow 102 (e.g., a gas stream) of radioactive material (e.g., radioactive discharge from a nuclear power plant) may enter system 100 (e.g., an “off-gas” system). Flow 102 may include radioactive material in the form of gases, liquids, and/or solids.
Flow 102 in first piping 103 may enter recombination subsystem 104, including preheater 106, recombiner 108, and first condenser 110. Preheater 106 may heat flow 102 to improve efficiency of a hydrogen recombination process in recombiner 108. Recombiner 108 may house the hydrogen recombination process. First condenser 110 may cool flow 102 to remove entrained water.
Flow 102 may continue in first piping 103 through second condenser 112 to further cool flow 102. By the time flow 102 leaves second condenser 112, it may be virtually without entrained water (e.g., “dry”).
Flow 102 in second piping 113 then may pass through first valve 114 and via third piping 115 to charcoal adsorption beds 116. After leaving charcoal adsorption beds 116, flow 102 in fourth piping 117 may proceed via second valve 118 to a stack (not shown) and the environment.
As shown in FIG. 1, flow 102 to charcoal adsorption beds 116 may bypass first valve 114 (or run in parallel with first valve 114) via fifth piping 119, third valve 120, sixth piping 121, guard vessel 122, seventh piping 123, and fourth valve 124. Flow 102 may bypass first valve 114 and charcoal adsorption beds 116 (or run in parallel with first valve 114 and charcoal adsorption beds 116) via fifth piping 119, third valve 120, sixth piping 121, guard vessel 122, eighth piping 125, and fifth valve 126. Flow 102 may bypass first valve 114, charcoal adsorption beds 116, and/or guard vessel 122 (or run in parallel with first valve 114, charcoal adsorption beds 116, and/or guard vessel 122) via ninth piping 127 and sixth valve 128. These and other potential combinations of paths for flow 102 in system 100 would be understood by a PHOSITA.
Charcoal adsorption beds 116 may provide the necessary Decontamination Factor (“DF”) of radioactive materials such as iodine and cesium. Removing water from flow 102 prior to passing through charcoal adsorption beds 116 may improve the DF (e.g., dewatering flow 102 before entering “dry” charcoal adsorption beds 116). Increasing the time flow 102 spends within charcoal adsorption beds 116 (e.g., residence time) may improve the DF.
System 100 is an example of an active system in that it requires, for example, pumps and associated supplies of power (not shown), external cooling (not shown), and the replacement of charcoal adsorption beds 116.
FIG. 2 is a block diagram of a related art system 200 for radioactive material capture.
As shown in FIG. 2, flow 202 in tenth piping 204 may pass through first isolation valve 206 and second isolation valve 208 to pressure vessel 210. Pressure vessel 210 may include lower high-speed venturi section 212 and upper metal fiber filter section 214.
Inside pressure vessel 210, tenth piping 204 may split into eleventh piping 216 and twelfth piping 218, both leading to high-speed venturi section 212. Eleventh piping 216 may be designed to support submerged venturi scrubber operation (e.g., below a surface of pool of water 220), while twelfth piping 218 may be designed to support unsubmerged venturi scrubber operation (e.g., above the surface of pool of water 220).
Flow 202 may enter pool of water 220 through a plurality of venturi nozzles (not shown), which may act as eductors to cause water from pool of water 220 to become entrained in flow 202. This entrainment may scrub aerosols and iodine from flow 202 and may store them in pool of water 220. Chemicals may be added to pool of water 220 to improve performance of lower high-speed venturi section 212. The water in pool of water 220 may be recirculated to the containment (not shown).
Scrubbed flow 222 may pass to upper metal fiber filter section 214. Upper metal fiber filter section 214 may include droplet separator (not shown), micro-aerosol filter (not shown), and iodine adsorption filter (not shown). Droplet return line 224 may route separated droplets back to pool of water 220.
Scrubbed and filtered flow 226 may pass via thirteenth piping 228, check valve 230, orifice 232, and rupture diaphragm 234 to a stack (not shown) and the environment.
Attainment of a high DF with system 200 may present problems. For example, the DF may be affected by the rate of flow 202, the temperature of pool of water 220, the pressure of pool of water 220, the residence time of gases in pool of water 220, the size of bubbles in the gases, and/or physical dimensions of pressure vessel 210, lower high-speed venturi section 212, and/or upper metal fiber filter section 214. System 200 also may present problems associated with initial cost, a large footprint, expense of operation, expense of maintenance, and/or internal blockage. Additionally, the DF of system 200 may not be able to be changed after installation of pressure vessel 210. Moreover, while in operation, pool of water 220 may require makeup water at least one per week (as stated by the manufacturer in sales brochures), so that operation of system 200 is not independent of required operator action.
A need exists for a fully passive systems, methods, and filters for radioactive material capture of gases, liquids, and/or solids to mitigate off-site release of radioactivity during a severe nuclear accident or any other time venting from the containment needs to be filtered.
Related art systems, methods, and/or filters for radioactive material capture are discussed, for example, in U.S. Pat. No. 5,688,402 to Green et al. (“the '402 patent”), as well as U.S. Patent Publication No. 2011/0132817 A1 to Gardner et al. (“the '817 publication”). The disclosures of the '402 patent and the '817 publication are incorporated in this application by reference in their entirety.